The present invention relates to an optical disk device and, more particularly, to an optical disk device that reduces a seek time.
Conventional optical disk devices prevent swings of a lens of a pickup at seeking, under position control and speed control, to perform high-speed seeking.
Here, a conventional optical disk device will be described with reference to FIG. 14. FIG. 14 is a block diagram illustrating a structure of a conventional optical disk device.
In FIG. 14, reference numeral 1 denotes an optical disk in which information is recorded on spiral tracks. A lens 2 focuses laser light on the optical disk 1, and is driven in axial and radial directions of the optical disk 1 by means of an actuator (not shown) provided on an upper part of the main body of an optical pickup 3. The optical pickup 3 applies laser light to the lens 2, and receives reflected light from the optical disk 1 to generate a signal that detects track crossing of the laser light on the optical disk 1 (hereinafter, abbreviated as a xe2x80x9ctrack crossing signalxe2x80x9d), a signal that detects deviation of the lens 2 from the center position on the optical pickup 3 (hereinafter, abbreviated as a xe2x80x9cposition detection signalxe2x80x9d), a signal that indicates defocusing of the laser light on the optical disk 1 (hereinafter, abbreviated as a xe2x80x9cfocus error signalxe2x80x9d), and a signal that indicates deviation of the laser light from the center of the track (hereinafter, abbreviated as a xe2x80x9ctracking error signalxe2x80x9d). A traverse driving means 4 drives the optical pickup 3 in the radial direction of the optical disk 1. A speed control means 5 measures a movement speed of the lens 2 on the basis of the track crossing signal that is generated by the optical pickup 3, and controls an actuator driving means 8 such that the movement speed of the lens 2 follows a target movement speed. A position control means 6 controls the actuator driving means 8 on the basis of the tracking error signal generated by the optical pickup 3 such that a midpoint of the lens 2 follows the center position of the optical pickup 3. A switching means 7 switches between outputs of the speed control means 5 and the position control means 6, to decide control input to the actuator driving means 8. The actuator driving means 8 controls the actuator provided on the optical pickup 3 to drive the lens 2 in the axial and radial directions of the optical disk 1. A system control means 9 reads information about a target speed of the optical pickup 3, which is previously set in a table corresponding to a speed profile 10, and controls the traverse driving means 4 and the actuator driving means 8 on the basis of the read information. The speed profile 10 is a table in which driving speed increasing/decreasing patterns for promptly moving the optical pickup 3 to a target track are described. A track lead-in means 30 guides the optical pickup 3 to the center position of the track on the optical pickup 1 on the basis of the tracking error signal, and it can make the optical pickup 3 follow the center of the track of the optical disk 1.
FIG. 15 is a diagram for explaining the speed control means 5. In this figure, the ordinate represents the movement speed of the lens 2 and the movement speed of the optical disk 1 varying due to eccentricity, and the abscissa represents the time.
When the traverse driving means 4 receives a command instructing a seek operation from the system control means 9, it moves the optical pickup 3 to a predetermined position, in accordance with a target speed that is previously set in the speed profile 10. At this time, the lens 2 that is provided on the optical pickup 3 via the actuator is moved while swinging as the optical pickup 3 is moved. Thus, the speed control means 5 performs the speed control such that the lens 2 has a fixed movement speed, thereby preventing swings of the lens 2 at the seek time, and realizing a prompt lead-in to the target track.
Actually, however, the optical disk 1 is also off-centered (radially swinging) while rotating, and there exists changes in the speed like SIN waves as shown in FIG. 15. Accordingly, the speed control means 5 controls the actuator driving means 8 for making the lens 2 follow the disk eccentricity shown by a broken line, and keeping a relative speed between the movement speed of the lens 2 and the movement speed of the optical disk 1 at a constant value. Therefore, the speed control means 5 that operates so as to make the movement speed of the lens 2 follow the changes in the speed of the optical disk 1 due to the eccentricity before leading into the target track immediately before the end of the seek operation, and to make the relative speed between the lens 2 and the optical disk 1 0 (zero) is effective.
On the other hand, as the speed control means 5 drives the traverse driving means 4 through the system control means 9, particularly when the traverse driving means 4 is sensitive to control inputs of a stepping motor and the like, the traverse driving means 4 sometimes responds too much to changes in the speed due to interference such as eccentricity or swings of the optical disk 1, so that step-out occurs at high-speed rotation, and the seek time is unfavorably delayed greatly.
FIG. 16 is a diagram for explaining the position control means 6 (lens midpoint control). In this figure, the ordinate represents the actuator sensitivity of the lens 2 at the seek time of the optical pickup 3, and the abscissa represents the amount of swings of the lens 2 (lens shift). This figure shows the state where the actuator sensitivity of the lens 2 varies according to the lens shift.
As shown in FIG. 16, a state in which the lens shift amount is zero, indicating that the lens 2 is located at the center of the optical pickup 3, is a state in which the actuator sensitivity is the highest. At this time, the response speed of the actuator to the control input from the actuator driving means 8 is the highest. Therefore, the lens 2 swings hard at the seek time when the optical pickup 3 is moving at high speeds, and thus, the position control means 6 that controls the lens 2 for being positioned at the center of the optical pickup 3 is effective. There are also merits that the position control means 6 controls only the actuator driving means 8, and the traverse driving means 4 can be controlled by the speed profile 10 independently.
On the other hand, the position control means 6 cannot control the movement speed of the lens 2 for following the movement speed of the optical disk 1 due to the eccentricity. Accordingly, there are some cases where the leading into the target track is delayed in the case of the optical disk 1 having larger eccentricity.
An operation of the conventional optical disk device that is constructed as described above will be described with reference to FIG. 17.
FIG. 17 is a diagram showing the operation of the conventional optical disk device immediately before an end of seeking. In this figure, the ordinate represents the sensitivity and movement speed of the lens 2, and the abscissa represents the seek time.
Initially, at high-speed movements of the lens 2 and the optical pickup 3 from when the seek operation is started until the optical pickup 3 reaches the vicinity of the target track, the switching means 7 is connected to the position control means 6 to control the lens shift, thereby keeping the lens in a high sensitivity state.
Then, when the optical pickup 3 reaches the vicinity of the target track, the switching means 7 is switched from the position control means 6 to the speed control means 5, and the lens 2 and the optical pickup 3 are moved at low speeds by the actuator driving means 6 and the traverse driving means 4, respectively, thereby enabling the movement speed of the lens 2 to follow the movement speed of the optical disk 1 due to the eccentricity. In this figure, reference S1 denotes the speed of the optical disk 1 due to the eccentricity (in reality, the optical disk 1 does not have a fixed speed but is swinging), and the lens 2 is controlled for following this speed S1.
When a rough seek operation for moving the optical pickup 3 to the vicinity of the target track on the optical disk by means of the traverse driving means 4 is completed, the optical disk device goes into a track lead-in state. Further, after the lead-in of the lens 2 to the target track is completed, the tracking servo control is performed to trace the target track.
At this time, the movement speed of the lens 2 controlled by the position control means 6 and the movement speed of the lens 2 controlled by the speed control means 5 do not always coincide with each other, and there is a difference E1 between the speeds. Then, a lens shift occurs to compensate the difference E1, and accordingly the actuator sensitivity is deteriorated up to K1. Thus, in order to speed up the seek time, it is desirable that the driving control of the actuator should be performed by means of the position control means 6, thereby turning the sensitivity of the lens 2 into a good condition as well as moving the optical pickup 3 as near the target track as possible, and thereafter, the speed control means 5 for controlling the movement speed of the lens 2 to follow the movement speed of the optical disk 1 due to the eccentricity should be selected to shorten the time (T1) for leading into the target track.
However, in the conventional optical disk device, there is a difference between the movement speed of the lens under control of the position control means 6 and the movement speed of the lens under control of the speed control means 5. Therefore, when the control input to the actuator driving means 8 is abruptly switched by the switching means 7 as a simple switch, the lens 2 unfavorably vibrates, and the control by the speed control means 5 is hardly stabilized, whereby the convergence takes a long time. Accordingly, the sensitivity of the actuator is deteriorated, resulting in a longer track lead-in time (T1).
The present invention has for its object to provide an optical disk device that reduces a track lead-in time associated with a seek time.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a 1st aspect of the present invention, there is provided an optical disk device including: an optical pickup for applying laser light to an optical disk via a lens, and receiving reflected light from the optical disk; an actuator for driving the lens in axial and radial directions of the optical disk on the optical pickup; a traverse driving means for driving the optical pickup in a radial direction of the optical disk so that a movement speed of the optical pickup becomes a preset target speed; a position control means for controlling the driving of the actuator so that the lens follows a center position of the optical pickup; a speed control means for controlling the driving of the actuator so that the lens has the target movement speed; a switching means for switching the control for the driving of the actuator between control by the position control means and control by the speed control means; and a system control means for controlling the switching means to select the position control means when a seek operation is started, while selecting the speed control means when the optical pickup comes to a vicinity of a target track on the optical disk, and in this optical disk device, the system control means controls the switching means so that the switching between the position control means and the speed control means is performed in stages. Therefore, the position control means is used immediately before the leading into the target track, and then the position control means is switched to the speed control means, whereby the lens can be made follow the eccentricity of the optical disk while maintaining a high actuator sensitivity, and accordingly the leading into the target track can be achieved in a shorter time.
According to a 2nd aspect of the present invention in the optical disk device of the 1st aspect, the system control means proportionally increases distribution of the control for the driving of the actuator by the speed control means according to the number of remaining tracks up to the target track while moving the optical pickup to the vicinity of the target track on the optical disk, thereby switching the control for the driving of the actuator from the control by the position control means to the control by the speed control means in stages. Therefore, the timing of the switching of the control for the actuator driving means from the control by the position control means to the control by the speed control means can be delayed, and further the lens can be made follow the eccentricity of the optical disk while maintaining a high actuator sensitivity, whereby the leading into the target track can be achieved in a shorter time.
According to a 3rd aspect of the present invention, in the optical disk device of the 1st aspect, the system control means controls the switching means at change of the preset target speed of the optical pickup. Therefore, the switching is performed at a time when a difference between the movement speed of the lens under control by the position control means and the movement speed of the lens under control by the speed control means is small, thereby suppressing vibrations of the lens, and achieving the leading into the target track in a shorter time.
According to a 4th aspect of the present invention, in the optical disk device of the 3rd aspect, the system control means proportionally increases distribution of the control for the driving of the actuator by the speed control means according to the number of points at which the target speed of the optical pickup is changed in the switching from the position control means to the speed control means by the switching means. Therefore, the vibrations of the lens can be suppressed, and the leading into the target track can be achieved in a shorter time.
According to a 5th aspect of the present invention, in the optical disk device of any of the 1st to 4th aspects, the system control means switches the control for the driving of the actuator from the control by the speed control means to the control by the position control means, when detecting that the speed control means does not operate normally during the control for the driving of the actuator performed by the speed control means. Therefore, running out of control of the traverse driving or the like due to abnormal operations of the speed control means can be prevented.
According to a 6th aspect of the present invention, the optical disk device of the 5th aspect includes a differentiation means for obtaining a differential value of the movement speed of the lens, which is measured by the speed control means, and deciding that the speed control means does not operate normally when the obtained differential value is larger than a predetermined value, and the system control means controls the switching means on the basis of a result of the decision by the differentiation means. Therefore, running out of control of the traverse driving or the like can be predicted and prevented when the movement speed of the lens greatly changes.
According to a 7th aspect of the present invention, the optical disk device of the 5th aspect includes a comparison means for obtaining a difference between the movement speed of the lens, which is measured by the speed control means, and the preset target speed, and deciding that the speed control means does not operate normally when the difference is larger than a predetermined value, and the system control means controls the switching means on the basis of a result of the decision by the comparison means. Therefore, running out of control of the traverse driving or the like can be predicted and prevented when the movement speed of the lens is out of the target speed.
According to an 8th aspect of the present invention, the optical disk device of the 5th aspect includes a focus error detection means for measuring an amount of focus deviation of the laser light on the optical disk when a focus error signal indicating a focus deviation of the laser light on the optical disk is detected from the reflected light received by the optical pickup, and deciding that the speed control means does not operate normally when the deviation amount is larger than a predetermined value, and the system control means controls the switching means on the basis of a result of the decision by the focus error signal detection means. Therefore, running out of control of the traverse driving or the like is predicted and prevented when the defocusing of the laser light on the optical disk occurs.
According to a 9th aspect of the present invention, in the optical disk device of the 1st aspect, the system control means adjusts a timing of the switching by the switching means from the position control means to the speed control means to be at a position nearer the target track. Therefore, the timing of the switching of the control for the actuator driving means from the control by the position control means to the control by the speed control means can be set at an optimum timing according to the environmental conditions, or variations of the optical disk device or the optical disk.
According to a 10th aspect of the present invention, the optical disk device of the 9th aspect includes an eccentricity detection means for measuring an amount of eccentricity of the optical disk on the basis of a track crossing signal indicating track crossing of the laser light, which is detected from the reflected light received by the optical pickup, and the system control means adjusts the timing of the switching by the switching means from the position control means to the speed control means to be at a position much nearer the target track when the eccentricity amount of the optical disk, measured by the eccentricity detection means, is smaller than a predetermined value. Therefore, the lens can be made follow the eccentricity of the optical disk at the seek time while maintaining a higher actuator sensitivity, whereby the leading into the target track can be achieved in a shorter time.
According to an 11th aspect of the present invention, in the optical disk device of the 9th aspect, the system control means adjusts the timing of the switching by the switching means from the position control means to the speed control means to be at a position further nearer the target track when the control for the driving of the actuator by the speed control means has been performed normally and a next movement of the optical pickup to the target track is performed. Therefore, the lens can be made follow the eccentricity of the optical disk at the next seek time while maintaining a further higher actuator sensitivity, whereby the leading into the target track can be achieved in a shorter time.
According to a 12th aspect of the present invention, in the optical disk device of the 9th aspect, when the optical pickup is led into the target track after a rough seek operation for moving the optical pickup to a position near the target track on the optical dick has been finished, the system control means counts the number of re-leading processes when leading of the optical pickup into the track has failed and then re-leading is performed, and adjusts the timing of the switching by the switching means from the position control means to the speed control means to be at a position further nearer the target track at a next movement of the optical pickup to the target track on the optical disk, when the counted number of re-leading processes is smaller than a preset number after the leading operation has been finished. Therefore, the lens can be made follow the eccentricity of the optical disk at the next seek time while maintaining a further higher actuator sensitivity, whereby the leading into the target track can be achieved in a shorter time.
According to a 13th aspect of the present invention, in the optical disk device of any of the 9th to 12th aspect, the system control means judges a movement direction in which the optical pickup is moved toward the target track on the optical disk, and sets timings of the switching by the switching means from the position control means to the speed control means adaptively to an inner circumference direction and an outer circumference direction of the optical disk, respectively. Therefore, an optimum timing can be set according to the movement directions of the optical pickup and the lens.
According to a 14th aspect of the present invention, in the optical disk device of the 1st aspect, the switching means includes a first shift register for multiplying an output signal of the speed control means by xe2x80x9cxcex1xe2x80x9d; a second shift register for multiplying an output signal of the position control means by xe2x80x9c(1xe2x88x92xcex1)xe2x80x9d; and an adder for adding output signals of the first and second shift registers, and the system control means gradually increases a value of xe2x80x9cxcex1xe2x80x9d of the first shift register to gradually increase allocation of control for driving the actuator by the speed control means over control for driving the actuator by the position control means. Therefore, the switching means can be implemented with a simple construction.
According to a 15th aspect of the present invention, in the optical disk device of the 1st aspect, a semiconductor element in which the speed control means, the position control means and the switching means are integrated. Therefore, high-speed operation processing can be performed without requiring additional hardware, whereby smooth switching between the speed control means and the position control means can be realized with a smaller delay due to the operation processing.